Magnetron sputtering coating device, a nano-multilayer film, and the preparation method thereof

ABSTRACT

A magnetron sputtering coating device includes a deposition chamber, sputtering cathodes, a rotating stand within the deposition chamber, a support platform on the rotating stand, a first rotation system for driving the rotating stand to rotate around a central axis of the rotating stand, and a baffle fixed on the rotating stand. The sputtering cathodes are arranged around and perpendicular to the rotating stand.

CROSS REFERENCE OF RELATED APPLICATIONS

This application claims the benefit of Chinese Patent Application No.201210151152.2, filed on May 15, 2012, and Chinese Patent ApplicationNo. 201220218296.0, filed on May 15, 2012, which are incorporated byreference in their entirety.

TECHNICAL FIELD

The present invention relates to a material preparation field,particularly to a device for preparation of a nano-multilayer film, anano-multilayer film and the preparation method thereof.

BACKGROUND

Vacuum magnetron sputtering technology has been widely used for coatingsurfaces of substrates. For example, such technology can be used forcoating such as diamond-like carbon (DLC) material on surfaces ofmedical surgical equipment, human implantation medical materials, andengineering tools. The coating will significantly increase hardness andwear resistance of the substrate.

Because a diamond-like carbon material has a large internal stress, anddoes not have a high binding force with metal or alloy materials, it isprone to rupture or peeling under a high load or load impact. Inparticular, if such coatings are used on a human implantation product,the peeling of diamond-like carbon may produce debris, which willaggravate the wear of the implantation product and reduce the servicelife of the product.

In order to resolve the above problems, the present disclosure providesa nano-multilayer film, which can increase the wear resistance of thesubstrate, increase the binding force with the substrate, and improvelubricity.

SUMMARY

The present disclosure provides a magnetron sputtering coating device.According to some embodiments, the magnetron sputtering coating deviceincludes a deposition chamber, a rotating stand positioned within thedeposition chamber and having a rotating axis, two first sputteringcathodes and a second sputtering cathode located on a circumferenceconcentric with the rotating axis. The second sputtering cathodecontains a material different from the two first sputtering cathodes.The magnetron sputtering coating device may further include a bafflefixed on the rotating stand and divides the deposition chamber into atleast two areas. The baffle separate at least one first sputteringcathode into one area, and the second sputtering cathode into anotherarea.

The present disclosure also provides a method for preparing a multilayerfilm on a substrate. According to some embodiments, the method forpreparing a multilayer film on a substrate includes providing at leastone first sputtering cathode in a deposition chamber, providing at leastone second sputtering cathode in the deposition chamber. The secondsputtering cathode includes a sputtering material that is different fromthe first sputtering cathode. The method may further includes providinga first current to the at least one first sputtering cathode forsputtering the substrate, and increasing the first current gradually,providing a second current to the at least one second sputtering cathodefor sputtering the substrate and decreasing the second currentgradually, and rotating the substrate within the deposition chamber toalternatively sputter the substrate with the at least one firstsputtering cathode or the at least one second sputtering cathode.

The present disclosure further provides a multilayer film prepared bymagnetron sputtering coating. According to some embodiments, themultilayer film prepared by magnetron sputtering coating includes atransition layer on a substrate. The transition layer includes atitanium layer and a mixed layer of titanium carbide and quasi-graphiteon the titanium layer. The multilayer film may further includes acomposite layer on the transition layer. The composite layer includes amultilayer structure with a quasi-graphite layer and a diamond-likecarbon layer alternately laminated. The quasi-graphite layer includes60% of materials by mass with a sp2 bond and the diamond-like carbonlayer includes 70% of materials by mass with a sp3 bond. The multilayerfilm may further includes a diamond-like carbon layer on the compositelayer. In the multilayer film, in a direction from the substrate to thediamond-like carbon layer, the mass percentage of titanium in the mixedlayer of titanium carbide and quasi-graphite is gradually decreased,while the mass percentage of carbon is gradually increased.

BRIEF DESCRIPTIONS OF THE DRAWINGS

The above and/or additional aspects and advantages of the presentinvention will become obvious and comprehensible from the followingdescription of the examples with reference to the drawings.

FIG. 1 is a stereoscopic schematic view of a magnetron sputteringcoating device according to an example of the present disclosure.

FIG. 2 is a top schematic view of the magnetron sputtering coatingdevice as shown in FIG. 1.

FIG. 3 is a top schematic view of the magnetron sputtering coatingdevice according to another example of the present disclosure.

FIG. 4 is a sectional schematic view of a nano-multilayer film incombination with a metal material according to an example of the presentdisclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

For better understanding the technical solution and beneficial effectsof the present invention, the examples of the present invention will bedescribed in detail below. The examples described below with referenceto the drawings are exemplary only for explanation rather thanrestriction of the present invention.

FIG. 1 and FIG. 2 show a stereoscopic and top structural schematic viewof a magnetron sputtering coating device according to an example of thepresent disclosure. According to some embodiments, the magnetronsputtering coating device includes a deposition chamber 100, a rotatingstand 102, sputtering cathodes, and a support platform 140, as well as afirst rotation system (not shown in the drawing) for driving therotating stand 102 to rotate around a central axis of the rotatingstand. The coating device may further include other suitable parts, forexample, a heating device, a temperature control system, a cooling watercirculation system, and a power supply system electrically connectedwith the sputtering cathode (not shown in the drawing).

In some embodiments, the sputtering cathodes include two firstsputtering cathodes 120 a and 120 b and one second sputtering cathode130, which are arranged on a circumference 104 concentric with therotating stand 102. The circumference 104 where the sputtering cathodesare located can either be an actual component such as an inner wall ofthe deposition chamber 100, or a virtual circumference such as anyposition between the rotating stand 102 and the inter wall of thedeposition chamber 100. In some embodiments, the two first sputteringcathodes 120 a and 120 b may be arranged parallel to each other and atpoints that equally divide the circumference 104. The second sputteringcathode 130 may be positioned in the middle of cathodes 120 a and 120 b,such that the second sputtering cathode 130 divides the arc between thetwo first sputtering cathodes 120 a and 120 b to two equal parts. Thearc between the two first sputtering cathodes 120 a and 120 b issubstantially 180°, while the arc between the second sputtering cathode130 and the first sputtering cathodes 120 a and 120 b is substantially90°. The first sputtering cathodes 120 a and 120 b can be a sputteringcathode of a certain chemical element. The second sputtering cathode canbe a sputtering cathode of another chemical element. The sputteringcathode material can be selected according to a specific product thatneeds to be coated. For example, the first sputtering cathodes can havea graphite target while the second sputtering cathode can have atitanium target. In some other examples, the first sputtering cathodescan have a graphite target while the second sputtering cathode can havea tantalum target.

In some other examples, the two first sputtering cathodes 120 a and 120b and the second sputtering cathode 130 can also be arranged on otherpositions on the circumference 140. For example, the arc between the twofirst sputtering cathodes 120 a and 120 b can be any angle ranging from180° to 240°. The second sputtering cathode 130 can be positioned in themiddle of the first sputtering cathodes 120 a and 120 b. The arc betweenthe second sputtering cathode 130 and the first sputtering cathode 120a/120 b can be any angle ranging from 90° to 120°. In the example shownin FIG. 3, the arc between the second sputtering cathode 130 and thefirst sputtering cathodes 120 a and 120 b is 120°.

In some embodiments, the rotating stand 102 may be a circular platform.The device may also include a baffle 110 fixed on the rotating stand102. The baffle 110, which may be a plate, can be made from titanium,aluminum, stainless steel and the like or a combination thereof. Asshown in FIG. 1, the baffle 110 is positioned along a diameter of therotating stand 102 and is arranged perpendicular to the rotating stand102. The baffle 110 divides the rotating stand 102 into two mutuallyindependent areas 102-1 and 102-2. In some embodiments, both ends of thebaffle 110, in the direction perpendicular to the rotating stand (thedirection of the Z axis), are beyond both ends of the sputteringcathodes 120 a, 120 b and 130. The baffle 110 blocks one or more of thesputtering cathodes 120 a, 120 b and 130 in a certain area, and allowsthe coating of certain sputtering cathodes in the opposing area. Inorder to achieve a better blocking effect, the baffle 110 may have awidth bigger than the diameter of the rotating stand 102, where thewidth refers to the length of the baffle along the diameter of therotating stand 102. In some embodiments, the distance “d” between thebaffle 110 and a closest point on the circumference of the supportplatform 140 where the sputtering cathode is located is 2-10 cm.

The rotating stand 102 may be provided with a first rotation system (notshown in the drawing) for driving the rotating stand 102 to rotatearound a central axis of the rotating stand 102. The rotating stand 102and the baffle 110 can both rotate around the central axis of therotating stand 102. When the rotating stand 102 rotates to a position,e.g. the position as shown in FIG. 2, with the blocking of the baffle110, an area 102-1 of the rotating stand 102 is exposed to the firstsputtering cathode 120 a (e.g., the graphite target) and the secondsputtering cathode 130 (the titanium target), allowing the product (orthe substrate) to be coated in the area 102-1 to be coated with a filmof carbon:titanium carbide (a mixed layer of carbon with titaniumcarbide); while another area 102-2 of the rotating stand is exposed tothe first sputtering cathode 120 b (the graphite target), thus allowingthe product in the area 102-2 to be coated with a carbon film. With therotation of the rotating stand 102, the product in different areas willbe coated alternately with the carbon:titanium carbide film and thecarbon film, thus realizing the coating of the product with anano-multilayer film. The thickness of a single layer can be controlledby adjustment of the rotational speed of the rotating stand.

In some other examples, the baffle 110 can also be placed at otherpositions on the rotating stand 102, but not necessarily along thediameter. The baffle 110 may be a bent plate or any other shape thatdivides the rotating stand 102 into two separate areas.

The device may further include a second rotation system for driving thesupport platform 140 to rotate around the central axis of the supportplatform 140. As shown in FIG. 1, multiple support platforms 140 can bearranged on the rotating stand 102 on a support rod 160. The supportplatforms 140 can be positioned at intervals on the same support rod160. The support platform 140 is used to support the substrate (orproduct) 150 to be processed, which can be uniformly arranged on thecircumference of the support platform 140. With the rotation of thesupport platform 140 around its axis, the coating on each of theproducts to be coated on the support platform 140 can be uniform.

In some other embodiments, four sputtering cathodes (not shown in thedrawing) can be used around the rotating stand 102. The sputteringcathodes can include two first sputtering cathodes and two secondsputtering cathodes. The two first sputtering cathodes can be arrangedopposite to each other, and the two second sputtering cathodes can bearranged opposite to each other. The four sputtering cathodes can bearranged at equal intervals on a circumference. In some embodiments,during the preparation of the multilayer film, one of the secondsputtering cathodes can be kept idle. The corresponding parameters suchas the target current and voltage may be set for the two firstsputtering cathodes and one of the second sputtering cathodes instead offor the other second sputtering cathode, which is not used forsputtering and in an idle state. In the example, although foursputtering cathodes are arranged, they may not be used for sputtering atthe same time.

The substrate to be coated can either be human implantation equipmentsuch as a bone articular head or acetabular cup, or be other substratessuch as engineering items. The substrate can be made of metal or alloymaterials or other materials.

The present disclosure also provides a method of coating a substrateusing the above-described magnetron sputtering coating devices.According to some embodiments, the method may include a first, second,and third sputtering stage. In the first sputtering stage, a workingcurrent of two first sputtering cathodes may be set to 0. A secondsputtering cathode is set to have a working current of a firstpredetermined current value and to be at a constant voltage mode. Theworking bias voltage is kept at a first predetermined bias voltage andthen the sputtering of a first predetermined duration is performed.Then, all sputtering cathodes are set to be at a constant voltage mode,and the working bias voltage is kept at a second predetermined biasvoltage. The working current of the two first sputtering cathodes,starting from an initial working current I1, is increased by ΔI1 atintervals of a first time interval T1, until reaching a secondpredetermined current value; the working current of the secondsputtering cathode, starting from the first predetermined current value,is decreased by ΔI2 at intervals of a second time interval T2, untilreaching a third predetermined current value.

In the second sputtering stage, all sputtering cathodes are set to be ata constant voltage mode, and the working bias voltage is kept at thesecond predetermined bias voltage. The working current of the secondsputtering cathode is set to and kept at a fourth predetermined currentvalue, and the working current of the first sputtering cathode is keptat the second predetermined current value or is set to and kept at afifth predetermined current value, and then the sputtering of a secondpredetermined duration is performed.

In the third sputtering stage, the working bias voltage is kept at thesecond predetermined bias voltage, the working current and voltage ofthe second sputtering cathode are set to be zero, and the firstsputtering cathode is kept at the working current of the secondsputtering stage or is set to and kept at a sixth predetermined currentvalue, and is kept at the constant voltage mode, and then the sputteringof a third predetermined duration is performed.

In some embodiments, a method for sputtering may use three sputteringcathodes, i.e., two first sputtering cathodes and one second sputteringcathode. In some other embodiments, another second sputtering cathodemay be used. Alternatively, the second sputtering cathode may be kept inan idle state and kept from being used in the preparation of thenano-multilayer film.

In some examples, the first sputtering cathodes of the magnetronsputtering coating device are titanium targets, and the secondsputtering cathode is a titanium target. First, the substrate to becoated (or the product to be coated) is put on the support platform 140in the deposition chamber 100. The deposition chamber 100 is vacuumed to2×10⁻⁴ Pa, with high pure argon introduced at a flow of 25 sccm. Then,the sputtering cathodes can be cleaned, and all the sputtering cathodescan be applied with a current of 0.4 A and a voltage of 500 V for 20minutes for cleaning.

The sputtering can then be performed. During the whole sputteringprocess, with the rotating stand 102 rotating at a constant speed, thesubstrate to be coated can also be rotated. More specifically, in afirst sputtering stage, the first predetermined current value of thesecond sputtering cathode can be set at 3.0-7.0 A, the voltage of thesecond sputtering cathode can be set at 800V. The first predeterminedbias voltage is 100-200V, and the first predetermined duration is 5-15min. The working bias voltage can be set at the second predeterminedvalue of 60-130V, wherein, the two first sputtering cathodes can be setat the initial working current I1 of 0.5-2.0 A. For the two firstsputtering cathodes, at a time interval of, for example, 5-15 min, theirworking current is increased by a certain value, for example, 0.5-1.5 A,until their working current is increased to a predetermined value, forexample, 4.0-7.0 A. For the second sputtering cathode, at a timeinterval of 5-15 min, its working current is decreased by a certainvalue, for example, 0.5-1.5 A, until its working current is decreased toa predetermined value such as 0-3.0 A. That is, during the sputteringprocess of the first stage, the current of the first sputtering cathodeis increased, e.g., stepwise, and the current of the second sputteringcathode is decreased, e.g., stepwise. The increase amount at each stepand the decrease amount at each step may be the same or different. Thetime intervals for each step for the first sputtering cathodes and thesecond sputtering cathode may be the same or different. The voltages forthe first sputtering cathodes and the second sputtering cathode may bekept constant in the whole process. After a period of sputtering, suchas for 50-100 min, the transition layer of 300-500 nm in thicknesscomposed of titanium film and a mixed layer of TiC and quasi-graphitecan be deposited onto the product, which can be a metal material.Because the current gradients of different targets are controlled in theprocess as described above, the mass percentage of Ti in the transitionlayer, from a layer in proximity to the metal material layer of theproduct to an upper layer, is decreased gradually from a higherpercentage to a lower percentage. The mass percentage of C is increasedgradually from a lower percentage. Thus, the binding force with thesubstrate, especially the substrates of metal or alloy materials, isincreased, and also its lubricity is increased gradually.

The mixed layer of titanium carbide and quasi-graphite refers to a layerof titanium carbide mixed with the quasi-graphite. That is, the mixedlayer contains both quasi-graphite and titanium carbide.

In the second sputtering stage, the working current of the firstsputtering cathode can be kept at 4.0-7.0 A, which is the lastpredetermined value of the first sputtering stage. The working currentof the first sputtering cathode can also be set and kept at a desiredpredetermined value such as 4.0-7.0 A. Meanwhile, the working current ofthe second sputtering cathode is set and kept at a desired predeterminedvalue such as 0.5-2.0 A. The voltage of all sputtering cathodes can bekept at a constant voltage of 800V. Sputtering can be performed for120-400 min, during which the working bias voltage is kept constant ofthe second predetermined bias voltage. Under these processingconditions, a composite layer of 1600-3300 nm is formed, which is amultilayer structure with the quasi-graphite layer (the content of sp²is about 60%) and the diamond-like carbon layer (the content of sp³ isabout 70%) alternately laminated.

In the third sputtering stage, the working bias voltage is kept atconstant of the second predetermined bias voltage. The voltage andcurrent of the second sputtering cathode are decreased to 0, making itidle, and the current of the two first sputtering cathodes is reset to adesired predetermined value such as 4.0-7.0 A. The current of the twofirst sputtering cathodes can also be kept at the current of the secondsputtering stage. The voltage of the two first sputtering cathodes iskept at a constant voltage of 800V. At this stage, sputtering isperformed for 15-20 min. Under these processing conditions, adiamond-like carbon top-layer film of about 100 nm is separately formedon the composite layer. The quasi-diamond of a high hardness makes thenano-multilayer film have better hardness and wear resistance. At thisstage, a nano-multilayer film in combination with the substrate isformed. The mass percentage of C in the formed nano-multilayer film is70%-97.6%, and the mass percentage of Ti is 2.4%-30%.

Furthermore, the present disclosure further provides a nano-multilayerfilm formed by the above-described method with the above-describeddevice, as shown in FIG. 4. The nano-multilayer film includes atransition layer 210 including a Ti film and a mixed layer of TiC andquasi-graphite on the substrate 200, a composite layer 212 ofalternately laminated diamond-like carbon and quasi-graphite on thetransition layer 210, and a diamond-like carbon top-layer film 214 onthe composite layer 212. The content of sp² in the quasi-graphite layeris 60% and the content of sp³ in the diamond-like carbon layer is 70%.In the direction from the substrate 200 to the diamond-like carbontop-layer film 214, the mass percentage of Ti in the mixed layer isgradually decreased, while the mass percentage of C is graduallyincreased. The composite layer 212 includes a multilayer structure withthe quasi-graphite layer 212 a and the diamond-like carbon layer 212 balternately laminated. There can be no limit to the number of thequasi-graphite layer and the diamond-like carbon layer in the compositelayer 212. The interface of the nano-multilayer film where thetransition layer is in combination with the substrate contains highercontent of titanium and lower content of carbon, thus having a higherbinding force with the substrate, also having a low internal stress andgood lubricity. Thus, the hardness and wear resistance are improvedthrough the diamond-like carbon top-layer.

In a specific example 1, the two first sputtering cathodes includegraphite targets, while the one second sputtering cathode includes atitanium target. The arc between the second sputtering cathode and oneof the first sputtering cathodes in the sputtering device issubstantially of 90°, the rotating stand has a rotational speed of 1.5rpm, and the substrate to be coated is rotated on its axis. All thesputtering cathodes are applied with a current of 0.4 A and a voltage of500 V for 20 minutes of sputter cleaning. Before coating, the substrateto be coated is put onto the supporting platform of the depositionchamber, and the deposition chamber is vacuumed to 2×10⁻⁴ Pa, with thehigh pure argon introduced at a flow of 25 sccm. Then the sputtering isperformed. Working bias voltage is set to 150V. One titanium target isset to have a constant voltage of 800V and a current of 7.0 A, andsputtering of 10 min is performed; then, working bias voltage isdecreased to 100V. The titanium target is kept at the constant voltageof 800V and has a current decreased stepwise by 1.0 A at intervals of 10min until down to 0. The two graphite targets are set to have a constantvoltage of 800V and a working current starting from 1.5 A and increasedstepwise by 1.0 A at intervals of 10 min until up to 7.0 A. Aftersputtering for 60 min, a transition layer composed of titanium film anda mixed layer of TiC and quasi-graphite (the ratio of C of the mixedlayer is increased gradually, while the ratio of Ti is decreasedgradually) of about 300 nm is deposited onto the substrate. And then,with the current and voltage of the two graphite targets kept constant,the current of the titanium target is increased to 1.0 A, with thevoltage kept at a constant voltage, the working bias voltage is kept at100 V. After 120 min, a composite layer of 1600 nm is formed on thetransition layer, comprising a quasi-graphite layer (the content of sp²is about 60%) and a diamond-like carbon layer (the content of sp³ isabout 70%) alternately laminated. The current and voltage of thetitanium target can be then decreased to 0, and the current of thegraphite target is increased to 7.0 A, with the voltage kept at 800 V.The working bias is kept at 100V. After 15 min, a diamond-like carbonfilm of 100 nm is formed on the composite layer. In the example, themass percentage of C in the formed nano-multilayer film is about 97%,and the mass percentage of Ti is about 3%.

In another specific example 2, the two first sputtering cathodes in thesputtering device are graphite targets, and the one second sputteringcathode is a titanium target. The arc between the second sputteringcathode and the first sputtering cathode is substantially of 90°, therotating stand has a rotational speed of 2.0 rpm, and the substrate tobe coated is rotated on its axis. Before coating, the substrate to becoated is put onto the support platform of the deposition chamber, andthe deposition chamber is vacuumed to 2×10⁻⁴ Pa, with the high pureargon introduced at a flow of 25 sccm. The sputtering cathodes areapplied with a current of 0.4 A and a voltage of 500 V for 20 minutes ofsputter cleaning. Then, the sputtering is performed. The working biasvoltage is set to 120V. One titanium target is set to have a constantvoltage of 800V and a current of 6.5 A, and sputtering of 5 min isperformed. The working bias voltage can then be decreased to 110V, andthe titanium target is kept at the constant voltage of 800V and has acurrent decreased stepwise by 1.0 A at intervals of 5 min until down to0. The two graphite targets being set to have a constant voltage of 800Vand a working current starting from 0.8 A and increased stepwise by 1.0A at intervals of 5 min until up to 6.5 A; After 80 min, a transitionlayer composed of titanium film and a mixed layer of TiC andquasi-graphite (the ratio of C of the mixed layer is increasedgradually, while the ratio of Ti is decreased gradually) of about 400 nmare deposited onto the substrate. With the current and voltage of thetwo graphite targets kept constant, the current of the titanium targetis increased to 1.5 A, with the voltage kept at the constant voltage.The working bias voltage is kept 110 V. After 180 min, a composite layerof 1800 nm is formed on the transition layer, comprising thequasi-graphite layer (the content of sp² is about 60%) and thediamond-like carbon layer (the content of sp³ is about 70%) alternatelylaminated. Then, the current and voltage of the titanium target aredecreased to 0. The current of the graphite target is increased to 6.5A, with the voltage kept at 800 V, and the working bias being kept at110V. After 15 min, a diamond-like carbon film of 100 nm is formed onthe composite layer. In the example, the mass percentage of C in theformed nano-multilayer film is about 92%, and the mass percentage of Tiis about 8%.

In still another specific example 3, the two first sputtering cathodesin the sputtering device are the graphite targets, while the one secondsputtering cathode is a titanium target. The arc between the secondsputtering cathode and the first sputtering cathode is substantially of90°, the rotating stand has a rotational speed of 2.5 rpm, and thesubstrate to be coated is rotated on its axis. Before coating, thesubstrate to be coated is put onto the support platform of thedeposition chamber, and the deposition chamber is vacuumed to 2×10⁻⁴ Pa,with the high pure argon introduced at a flow of 25 sccm. All thesputtering cathodes are applied with a current of 0.4 A and a voltage of500 V for 20 minutes of sputter cleaning. The sputtering is performed.The working bias voltage is set to 150V. One titanium target is set tohave a constant voltage of 800V and a current of 6.0 A, and sputteringof 12 min is performed. The working bias voltage can then be decreasedto 120V. The titanium target is kept at a constant voltage of 800V andhas a current decreased stepwise by 1.0 A at intervals of 12 min untildown to 0. The two graphite targets are set to have a constant voltageof 800V and a working current starting from 1.8 A and increased stepwiseby 1.0 A at intervals of 12 min until up to 6.0 A. After 100 min, atransition layer composed of titanium film and a mixed layer of TiC andquasi-graphite (the ratio of C of the mixed layer is increasedgradually, while the ratio of Ti is decreased gradually) of about 500 nmare deposited onto the substrate. Then, with the current and voltage ofthe two graphite targets kept constant, the current of the titaniumtarget is increased to 1.8 A, with the voltage kept at a constantvoltage. The working bias voltage is kept at 120 V. After 260 min, acomposite layer of 1900 nm is formed on the transition layer, comprisingthe quasi-graphite layer (the content of sp² is about 60%) and thediamond-like carbon layer (the content of sp³ is about 70%) alternatelylaminated. Then, the current and voltage of the titanium target aredecreased to 0. The current of the graphite target is increased to 6.0A, with the voltage kept at 800 V. The working bias is kept at 120V.After 15 min, a diamond-like carbon film of 100 nm is formed on thecomposite layer. In the example, the mass percentage of C in the formednano-multilayer film is about 86%, and the mass percentage of Ti isabout 14%.

An observation was made to the surface of the nano-multilayer film ofthe above specific examples 1-3 through a scanning electron microscope,finding that the surface of the nano-multilayer films had small surfaceroughness. The hardness of the nano-multilayer films was measured by ananoindentation instrument, with a load of 10 mN, a pressed depth beinggreater than 10 times of the surface roughness and smaller than 1/10 ofthe thickness of the nano-multilayer films, so as to guarantee theauthenticity and validity of the measured hardness. The longitudinalbinding force and the lateral binding force of the nano-multilayer filmswere evaluated through a standard indentation instrument and theautomatic scratch test. With a load of the indentation test being 150 Nand the radius of the indenter being 0.2 mm, no crack and delaminationwas found around the indentation, indicating that the nano-multilayerfilm had a high longitudinal binding force. The load was increasedgradually from 10 N to 85 N, with a sliding velocity of 10 mm/min. Therewas no crack and peeling around and at the edge of the scratch,indicating that the nano-multilayer film had a high lateral bindingforce.

The ball-disc friction and wear machine were used for determination ofthe friction and wear properties of the nano-multilayer film. Thegrinding ball was a Si₃N₄ ceramic ball having a hardness of 1500 HV anda diameter of 3 mm. The load was 10 N, the sliding velocity was 0.10m/s, and the friction duration was 30 min. The experiments were madeunder the conditions of room temperature, no lubrication, and humid air(50% relative humidity). In the testing process, the change of thefriction coefficient was automatically recorded. After the test, thewear volume was measured with a step meter, with the wear ratecalculated. Table 1 shows the hardness, average friction coefficient andwear rate of the nano-multilayer film of Examples 1, 2 and 3.

TABLE 1 Sectional binding force of Average Nano- Content nano-multilayerfilm friction multilayer of Ti with substrate (N) coefficient Wear ratefilm (at. %) Longitudinal Lateral (u) (m³/Nm) Example 1 3 >150 ≧95 0.0482.8 × 10⁻¹⁷ Example 2 8 >150 ≧95 0.052 2.3 × 10⁻¹⁷ Example 3 14 >150 ≧950.046 3.1 × 10⁻¹⁷

The nano-multilayer film of the present invention has a low frictioncoefficient, a high wear resistance and a high bonding force with thesubstrate of the product. In the nano-multilayer film of the specificexamples 1, 2 and 3, the average friction coefficients of their filmsare 0.048, 0.052 and 0.046, respectively, without obvious change of thefriction coefficient during the test process, indicating that thenano-multilayer film has a good friction stability, the surface weartrace of the nano-multilayer film being very shallow after the wear. Thewear rates of the nano-multilayer films of the specific examples 1, 2and 3 are 2.8×10⁻¹⁷, 2.3×10⁻¹⁷ and 3.1×10⁻¹⁷ m³/Nm, respectively,indicating that the nano-multilayer film has a good wear resistance.Moreover, the pits of the nano-multilayer films of the specific examples1, 2 and 3 formed under the load of 150 N have no crack, delamination orpeeling trace at the edge thereof. Under the load of 85 N, there is nocrack or peeling of the nano-multilayer film observed in the area and atthe edge of the scratch formed on the surface of the nano-multilayerfilm. The pit and scratch tests show that the nano-multilayer film hasexcellent bonding strength with the metal substrate.

What is described above is only the preferred embodiments of the presentinvention. It should be pointed out that, for those of ordinary skill inthe art, some improvements and amendments can further be made under thepremise of not departing from the principles of the present invention,and should also be regarded as being within the scope of protection ofthe present invention.

What is claimed is:
 1. A multilayer film prepared by magnetronsputtering coating comprising: a transition layer on a substrate, thetransition layer including a titanium layer and a mixed layer oftitanium carbide and quasi-graphite on the titanium layer; a compositelayer on the transition layer, the composite layer including amultilayer structure with a quasi-graphite layer and a diamond-likecarbon layer alternately laminated, wherein the quasi-graphite layerincludes 60% of materials by mass with a sp² bond and the diamond-likecarbon layer includes 70% of materials by mass with a sp³ bond; and adiamond-like carbon layer on the composite layer, wherein in a directionfrom the substrate to the diamond-like carbon layer, the mass percentageof titanium in the mixed layer of titanium carbide and quasi-graphite isgradually decreased, while the mass percentage of carbon is graduallyincreased.
 2. The multilayer film according to claim 1, wherein thetransition layer has a thickness of 300-500 nm.
 3. The multilayer filmaccording to claim 1, wherein the diamond-like carbon layer has athickness of 100-150 nm.
 4. The multilayer film according to claim 1,wherein the mass percentage of carbon in the multilayer film is70%-97.6%, and the mass percentage of titanium is 2.4%-30%.
 5. Themultilayer film according to claim 1, wherein the composite layer has athickness of 1600-3300 nm.
 6. A multilayer film prepared by magnetronsputtering coating comprising: a first layer on a substrate, the firstlayer including a titanium layer and a mixed layer of titanium carbideand a carbon material with a majority of the material having sp² bond onthe titanium layer; a second layer on the first layer, the second layerincluding a multilayer structure with a third layer and a forth layeralternately laminated, wherein the third layer includes 60% of materialsby mass with a sp² bond and the fourth layer includes 70% of materialsby mass with a sp^(a) bond; and a fifth layer formed by carbon on thesecond layer, wherein in a direction from the substrate to the fifthlayer, the mass percentage of titanium in the mixed layer is graduallydecreased, while the mass percentage of carbon is gradually increased.7. The multilayer film according to claim 5, wherein the first layer hasa thickness of 300-500 nm.
 8. The multilayer film according to claim 6,wherein the fifth layer has a thickness of 100-150 nm.
 9. The multilayerfilm according to claim 6, wherein the mass percentage of carbon in themultilayer film is 70%-97.6%, and the mass percentage of titanium is2.4%-30%.